I know Killzone 2 multiplayer is somewhat still active, but I'll talk about it as past, now that the new Killzone is coming.
Killzone 2 had great multiplayer, and emphasis on team-play was great. To win, people had to work as a team. However, people love to earn points. They want to be the top player in team. Strangely, they forget that winning would earn them 1.5x points, not contentrating on winning but securing more points in a short time, while waiting for other "suckers" on his team to complete the objectives. Sure, incapacitating enemy helps the team win, but this has to be done near the objective, not the other end of the map.
In KZ2, fragging was the single most effective way to earn points. To put it into If you killed 3 opponents with headshots in a body count objective, you earned more points that a person who had actually planted a bomb to score for the team. In the body-count objective, you may be killed 30 times, while killing 3, thereby making your team lose the body-count. But congratulations, you have earned more points than the guy that won the search&destroy (bomb-plant) objective.